Oxidized graphite is a product of hydrolysis of graphite intercalation compounds (GIC) with strong inorganic acids, for example, sulfuric or nitric acid.
Oxidized graphite is used as a base for producing foamed graphite, which is a very light-weight, chemically inert material that is essentially a heat-expanded graphite.
This material is obtained by rapidly heating oxidized graphite.
Oxidized graphite may be obtained by treating graphite in aqueous solutions of strong acids, for example, sulfuric or nitric acid, in the presence of oxidizing agents, or by electrochemical treatment.
To achieve a foaming effect, oxidized graphite is subjected to heat treatment at a temperature in the order of 900-1,000° C.
For example, U.S. Pat. No. 4,350,576 discloses a method for producing foamed graphite, comprising electrochemical processing by anodic oxidation of graphite in aqueous solutions of H2SO4 or HNO3 at a constant current density of less than 500 mA/cm2 for 6 to 7 hours, followed by washing with water, drying, and heat treatment.
The bulk density of foamed graphite obtained by this method is between 4 and 6 g/liter.
This known method is disadvantageous because of the considerable duration of electrochemical treatment, non-uniformity of the end product, unsatisfactory bulk density of the product, and absence of foaming capacity at relatively low temperatures (150-250° C.).
A number of publications that have come out in recent years disclose production of oxidized graphite, which has a low foaming temperature, for manufacturing foamed graphite. In particular, GB Patent No. 2,367,291 describes a method for producing oxidized graphite, which comprises preliminary treatment of feedstock graphite in organic acids of the general formula H(CH2)nCOOH, wherein n takes values of 0 to 5, followed by electrochemical treatment in an aqueous solution of 30-50% H2SO4 at a constant current density of up to 0.06 A/cm2, washing with water, drying, and heat treatment. Accordingly, the patent discloses a foamed graphite produced by this method at a bulk density of 3-5 g/liter. The foamed graphite is capable of foaming at low temperatures.
This known method is disadvantageous because the use of organic compounds at the preliminary treatment stage complicates the method significantly since it requires the use of additional equipment capable of distributing a small quantity of organic additive over the entire mass of feedstock graphite. But even in that case, the probability of the feedstock and, therefore, foamed graphite being non-uniform is very high. Besides, this processing method creates a problem of mixed acidic waste disposal, adding to the costs of the method.